The graphic arts industry has been evolving techniques of printing on a wide range of substrates. Many printing techniques involve one or a combination of "ink drying" techniques which utilize volatile organic compounds. As environmental awareness increases, there is an overall movement to reduce the emissions of volatile organic compounds.
The environmental pressure led to the development of inks which lack a volatile organic solvent on which are dried, or more appropriately cured, using either ultraviolet or electron beam radiation, thereby eliminating evaporation of volatile organic compounds. The customary ultraviolet and electron beam cured inks are not without flaw however. Many customary inks display poor color strength, weak fluorescence and fading. Indeed, the colored chromophores, especially fluorescent dyes, are susceptible to photodegradation when exposed to the ultraviolet radiation used in the curing process. The photodegradation results in a shift in the color of the chromophore and a loss in the color intensity.
Furthermore, many of the fluorescent colorants are either incompatible, or not dispersible within the photopolymerizable vehicle and therefore are not suitable for use in ultraviolet/electron beam cured inks. Thus the color selection of ultraviolet and electron beam curable fluorescent inks is limited.
Some ultraviolet curable inks have been developed which are capable of "wetting" conventional colored pigments and dyes into the photopolymerizable systems. However, the photopolymerizable wetting agents must first be synthesized, and the conventional pigment or dye then dispersed into the photopolymerizable system either through high shear, grinding, or milling operations. Also, many of these photopolymerizable wetting agents are synthesized using volatile organic solvents, which must be removed from the product. Furthermore, many of these photopolymerizable wetting agents render the ink suitable for only specific substrates and thus have limited applications.
It would be desirable to have fluorescent ink concentrates and fluorescent inks which are ultraviolet/electron beam curable, that do not contain nor require for synthesis volatile organic solvents, yet are solvent resistant when cured.